Degradation of poly(N-vinylcarbazole) by annealing under iodine pressure

After room temperature doping of poly(N-vinylcarbazole) by iodine, the powders are annealed at different temperatures (370, 470, and 570 K) for 24 h under vacuum or under iodine pressure. The obtained powders were studied by infrared absorption, x-ray photoelectron spectroscopy, x-ray diffraction, and nuclear magnetic resonance. Annealing of pure PVK powder increases the crystallization quality of the sample. Annealing with iodine induces progressive polymer degradation. At 570 K under iodine pressure the PVK is totally destroyed. The aromatic rings and the C(SINGLEBOND)N bonds have disappeared. NH₄I crystallites have formed, embeded in a degraded, cross-linked polymer matrix. © 1996 John Wiley & Sons, Inc.     

The effect of conjugation length distribution on the properties of modified PPV

The aim of this work was to demonstrate the optical properties of a copolymer involving alternating poly(para-phenylene–vinylene) and ether groups derived from the conjugation length distribution. For this, the time-dependent density functional theory (TD-DFT) was used. Thus, different conjugation lengths were considered, where the correlation of the corresponding theoretical spectra, including Raman, optical absorption and photoluminescence, allows us to conclude that the conjugation length distribution is caused by a random distribution of the ether blocks. The weight of each conjugation length representing its contribution is shown by the use of the Raman spectra. Furthermore, the theoretical spectra arising from the response of different conjugation lengths are obtained and compared with the experimental ones.     

Modelling and Simulation of Degassing Process

This work deals with the modelling and simulation of a degassing process mainly used for extruders in polymer industry. The numerical simulations are done with finite-volume method using OpenFOAM for a 2D single screw extruder. The material parameters have been all chosen for a PDMS-Pentane polymer mixture so that the results could be compared with the available experiments already performed for this mixture [1]. In addition to experiments, the numerical results will be compared with an analytical solution derived from Danckwerts' model [2][3]. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The anodic reactivity of 4,4′-dimethoxychalcone: a synthetic and mechanistic investigation

The anodic oxidation of the 4,4′-dimethoxychalcone (DMC) was investigated by different electrochemical methods at a platinum working electrode and in acetonitrile as a solvent. The DMC exhibited a single irreversible anodic peak around 1.6 V versus Ag/AgCl. On the time scale of cyclic voltammetry experiments, the highly reactive radical cation issued from the first electron transfer underwent a second order rate-limiting reaction. The potential imposed electrolyses of DMC led to the formation of a semi-conducting oligomer with 40 % yield. Using different physico-chemicals methods, the structural study confirmed the formation of an o-phenylenevinylene oligomer. The values of the corresponding optical and electrochemical band gaps were calculated to be 3.15 and 2.86 eV, respectively. Finally, a mechanism for the DMC electro-oligomerization was proposed on the basis of the obtained results.     

Characterization of Cobalt(III) Hydroxamic Acid Complexes Based on a Tris(2-pyridylmethyl)amine Scaffold: Reactivity toward Cysteine Methyl Ester

Six Co(III) complexes based on unsubstituted or substituted TPA ligands (where TPA is tris(2-pyridylmethyl)amine) and acetohydroxamic acid (A), N-methyl-acetohydroxamic acid (B), or N-hydroxy-pyridinone (C) were prepared and characterized by mass spectrometry, elemental analysis, and electrochemistry: [Co(III)(TPA)(A-2H)](Cl) (1a), [Co(III)((4-Cl(2))TPA)(A-2H)](Cl) (2a), [Co(III)((6-Piva)TPA)(A-2H)](Cl) (3a), [Co(III)((4-Piva)TPA)(A-2H)](Cl) (4a) and [Co(III)(TPA)(B-H)](Cl)(2) (1b), and [Co(III)(TPA)(C-H)](Cl)(2) (1c). Complexes 1a-c and 3a were analyzed by (1)H NMR, using 2D ((1)H, (1)H) COSY and 2D ((1)H, (13)C) HMBC and HSQC, and shown to exist as a mixture of two geometric isomers based on whether the hydroxamic oxygen was trans to a pyridine nitrogen or to the tertiary amine nitrogen. Complex 3a exists as a single isomer that was crystallized. Its crystal structure revealed the presence of an H-bond between the pivaloylamide and the hydroximate oxygen. Complexes 1a, 2a, and 4a are irreversibly reduced beyond -900 mV versus SCE, while complexes 1b and 1c are reduced at less negative values of -330 and -190 mV, respectively. The H-bond in 3a increased the redox potential up to -720 mV. Reaction of complex 1a with l-cysteine methyl ester CysOMe was monitored by (1)H NMR and UV-vis at 2 mM and 0.2 mM in an aqueous buffered solution at pH 7.5. Complex 1a was successively converted into an intermediate [Co(III)(TPA)(CysOMe-H)](2+), 1d, by exchange of the hydroximate with the cysteinate ligand, and further into Co(III)(CysOMe-H)(3), 5. An authentic sample of 1d was prepared and thoroughly characterized. A detailed (1)H NMR analysis showed there was only one isomer, in which the thiolate was trans to the tertiary amine nitrogen.     

Pillar[3]trianglamines: deeper cavity triangular macrocycles for selective hexene isomer separation

The separation of α-olefins and their corresponding isomers continues to be a big challenge for the chemical industry due to their overlapping physical properties and low relative volatility. Herein, pillar[3]trianglamine (P-TA) macrocycles were synthesized for the molecular-sieving-like separation of 1-hexene (1-He) selectively over its positional isomer trans-3-hexene (trans-3-He) in the vapor and liquid state. This allyl-functionalized macrocycle features a deeper cavity compared to the previously reported trianglamine host molecules. Solid–vapor sorption experiments verified the successful separation of 1-He from an equimolar mixture of 1-He and trans-3-He. Single-crystal structures and powder X-ray diffraction patterns suggest that this selective adsorption arises from the formation of a thermodynamically stable host–guest complex between 1-He and P-TA. A reversible transformation between the nonporous guest-free structure and the guest-containing structure shows that 1-He separation can be carried out over multiple cycles without any loss of performance. Significantly, P-TA can separate 1-He directly from a liquid isomeric mixture and thus P-TA modified silica sieves (SBA-15) showed the ability to selectively separate 1-He when utilized as a stationary phase in column chromatography. This capitalizes on the prospects of employing macrocyclic hosts as molecular recognition units in real-life separations for sustainable and energy-efficient industrial practices.

Crystalline allyl-functionalized trianglamine macrocycles (P-TA) that show a pillared-like cavity were successfuly prepared and employed for the robust molecular sieving of 1-He from vapor and liquid (in solution) isomeric mixtures.     

Synthesis and Spectral Characterization of New 2-(5-Aryl-4H-1,2,4-triazol-3-yl)-1H-isoindole-1,3(2H)-dione Derivatives

Russian Journal of Organic Chemistry - A series of novel 2-(5-aryl-4H-1,2,4-triazol-3-yl)-1H-isoindole-1,3(2H)-diones were synthesized in three steps. In the first step, treatment of substituted...